Vacuum IG window units are known in the art. For example, see U.S. Pat. Nos. 5,664,395, 5,657,607, and 5,902,652, the disclosures of which are all hereby incorporated herein by reference.
FIGS. 1-2 illustrate a conventional vacuum IG unit (vacuum IG unit or VIG unit). Vacuum IG unit 1 includes two spaced apart glass substrates 2 and 3, which enclose an evacuated or low pressure space 6 therebetween. Glass sheets/substrates 2 and 3 are interconnected by peripheral or edge seal of fused solder glass 4 and an array of support pillars or spacers 5.
Pump out tube 8 is hermetically sealed by solder glass 9 to an aperture or hole 10 which passes from an interior surface of glass sheet 2 to the bottom of recess 11 in the exterior face of sheet 2. A vacuum is attached to pump out tube 8 so that the interior cavity between substrates 2 and 3 can be evacuated to create a low pressure area or space 6. After evacuation, pump-out tube 8 is melted to seal the vacuum. Recess 11 retains sealed tube 8. Optionally, a chemical getter 12 may be included within recess 13.
Conventional VIG units, with their fused solder glass peripheral seals 4, have been manufactured as follows. Glass frit in a solution (ultimately to form solder glass edge seal 4) is initially deposited around the periphery of glass substrate 2. The other glass substrate 3 is brought down over top of substrate 2 so as to sandwich spacers 5 and the glass frit/solution therebetween. The entire assembly including sheets 2, 3, the spacers 5, and the seal material is then heated to a temperature of approximately 500° C., at which point the glass frit melts, wets the surfaces of the glass sheets 2, 3, and ultimately forms hermetic peripheral or edge seal 4. This approximately 500° C. temperature is maintained for from about one to eight hours. After formation of the peripheral/edge seal 4 and the seal around tube 8, the assembly is cooled to room temperature. It is noted that column two of U.S. Pat. No. 5,664,395 states that a conventional vacuum IG processing temperature is approximately 500° C. for one hour. Inventor Collins of the '395 patent states in “Thermal Outgassing of Vacuum Glazing,” by Lenzen, Turner and Collins, that “the edge seal process is currently quite slow: typically the temperature of the sample is increased at 200° C. per hour, and held for one hour at a constant value ranging from 430° C. and 530° C. depending on the solder glass composition.” After formation of edge seal 4, a vacuum is drawn via the pump-out tube 8 to form low pressure space/gap/cavity 6.
Unfortunately, the aforesaid high temperatures and long heating times of the entire VIG assembly utilized in the formulation of edge seal 4 are undesirable, especially when it is desired to use a heat strengthened or tempered glass substrate(s) 2, 3 in the VIG unit. As shown in FIGS. 3-4, tempered glass loses temper strength upon exposure to high temperatures as a function of heating time. Moreover, such high processing temperatures may adversely affect certain low-E coating(s) that may be applied to one or both of the glass substrates in certain instances.
FIG. 3 is a graph illustrating how fully thermally tempered plate glass loses original temper upon exposure to different temperatures for different periods of time, where the original center tension stress is 3,200 MU per inch. The x-axis in FIG. 3 is exponentially representative of time in hours (from 1 to 1,000 hours), while the y-axis is indicative of the percentage of original temper strength remaining after heat exposure. FIG. 4 is a graph similar to FIG. 3, except that the x-axis in FIG. 4 extends from zero to one hour exponentially.
Seven different curves are illustrated in FIG. 3, each indicative of a different temperature exposure in degrees Fahrenheit (° F.). The different curves/lines are 400° F. (across the top of the FIG. 3 graph), 500° F., 600° F., 700° F., 800° F., 900° F., and 950° F. (the bottom curve of the FIG. 3 graph). A temperature of 900° F. is equivalent to approximately 482° C., which is within the range utilized for forming the aforesaid conventional solder glass peripheral seal 4 in FIGS. 1-2. Thus, attention is drawn to the 900° F. curve in FIG. 3, labeled by reference number 18. As shown, only 20% of the original temper strength remains after one hour at this temperature (900° F. or 482° C.). Such a significant loss (i.e., 80% loss) of temper strength is of course undesirable.
In FIGS. 3-4, it is noted that much better temper strength remains in a thermally tempered glass substrate when it is heated to a temperature of 800° F. (about 428° C.) for one hour as opposed to 900° F. for one hour. Such a glass sheet retains about 70% of its original temper strength after one hour at 800° F., which is significantly better than the less than 20% when at 900° F. for the same period of time. Thus, exposing the entire glass substrates to high temperatures typically causes them to lose at least some of the strength provided during heat treatment (HT). For example, tempered soda lime glass substrates sometimes actually may significantly de-temper at high temperatures.
Another advantage associated with not heating up the entire unit for too long is that lower temperature spacer/pillar materials may then be used. This may or may not be desirable in some instances.
Even when non-tempered glass substrates are used, the high temperatures applied to the entire VIG assembly may melt the glass or introduce stresses. These stresses may increase the likelihood of deformation of the glass and/or breakage.
Thus, it will be appreciated that there is a need in the art for a VIG unit, and corresponding method of making the same, where a structurally sound hermetic edge seal may be provided between opposing glass sheets. There also exists a need in the art for a VIG unit including tempered glass sheets, wherein the peripheral seal is formed such that the glass sheets retain more of their original temper strength than with a conventional vacuum IG manufacturing technique where the entire unit is heated in the same manner in order to form an edge seal.
Certain example embodiments of this invention relate to providing an infrared (IR) absorbing element(s) such as a clip or clamp proximate an edge portion of a VIG assembly during formation of an edge seal. The IR absorbing element(s) directly contacts at least one of the glass substrates of the assembly, which glass substrates may be thermally tempered. The IR absorbing element(s) proximate the edge portion of the VIG assembly, and proximate the edge seal material, is thermally conductive and absorbs more IR than does the glass or edge material alone. Thus, the IR absorbing element(s) absorb applied IR radiation and heat up during an edge seal formation process, and because the element(s) is/are thermally conductive and in contact with at least one of the glass substrates the element(s) causes/cause heat to be transferred from the element(s) to the adjacent glass substrate(s) and to the adjacent edge seal material thereby helping the edge seal material to heat up faster during the edge seal formation process. This localized heating of the edge seal area proximate the perimeter of the assembly and proximate the IR absorbing element(s) causes a thermal differential across the assembly so that during the edge seal formation process the temperatures of the glass substrate(s) are higher proximate the edge seal area than at other areas across the assembly such as a central area of the VIG assembly. This allows heat to be concentrated in areas where the frit material is to be melted in order to form the edge seal. The reduced temperatures at other areas (e.g., central area) of the VIG assembly allow the glass substrates (e.g., thermally tempered glass substrates) to retain more strength compared to if the entire assembly were equally heated to the same high temperatures, and/or allows the edge seal to be formed in a shorter period of time.
In certain example embodiments of this invention, there is provided a method of making a vacuum insulating glass (VIG) window unit, the method comprising: having a VIG assembly including first and second substantially parallel spaced-apart glass substrates with a plurality of spacers therebetween, the first and second glass substrates each including one or more edge portions to be sealed, a frit for forming an edge seal being provided at least partially between the first and second glass substrates; providing a plurality of infrared (IR) absorbing clamps around a peripheral area of the VIG assembly, the IR absorbing clamps clamping the first and second glass substrates together and overlapping at least part of the frit for forming the edge seal; and directing IR energy from at least one IR source toward the frit for forming the edge seal and toward the IR absorbing clamps during a process of melting the frit so as to form the edge seal, the IR absorbing clamps absorbing IR radiation from the at least one IR source and transferring heat to at least one of the glass substrates and to the frit in order to help melt the frit when forming the edge seal.
In certain example embodiments of this invention, there is provided vacuum insulating glass (VIG) assembly, comprising: first and second substantially parallel spaced-apart glass substrates with a plurality of spacers therebetween, wherein the first and second substrates each include one or more edge portions to be sealed; a frit provided at least partially between the first and second glass substrates for sealing said one or more edge portions to be sealed, and a plurality of infrared (IR) absorbing clamps at a peripheral area of the VIG assembly, the IR absorbing clamps clamping the first and second glass substrates together and overlapping at least part of the frit for forming the edge seal.
The features, aspects, advantages, and example embodiments described herein may be combined to realize yet further embodiments.